Image forming devices such as copiers, printers, and facsimile machines include media transport systems that employ baffles, drive rollers, and idler rollers to guide and drive media along a media transport path. A baffle is typically made of sheet metal or plastic, and includes cutout sections. The drive and idler rollers protrude through these cutout sections and are responsible for driving the media via a nip formed by a pair of rollers. Contact between a leading edge of a sheet and a nip roller is known to generate torque spikes of magnitudes that depend upon factors such as the baffle to nip roller geometry, media stiffness, and thickness. It is, therefore, desirable to configure the baffle to nip roller entrance geometry for smoothly guiding the sheet into a tangent plane of the nip, thus, minimizing sheet disturbances and the sheet drive-torque spikes.
In curved media transports, especially while transporting very stiff, thick, or heavy media, such as those employed in folding carton-packaging applications, the leading edge of a sheet is naturally biased against the outer baffle. Such a natural bias may be employed to advantage by positioning the nip tangent plane near the outer baffle surface to ensure optimal entry of the sheet into the nip. In practical systems, however, baffle characteristics such as length, flatness, deflection, and positioning relative to nip rollers, introduce tolerances and limit optimal positioning of the nip relative to the baffle. As it is undesirable to have the nip positioned below the surface of the baffle, the nip must be nominally positioned above the baffle surface by a dimension based on the total tolerances of the system. Media transport module and baffle manufacturers have endeavored to achieve tight overall tolerances by controlling individual tolerances, as well as adding stiffeners to the baffle for producing precise, flat, and rigid parts that do not deflect under load. Such measures, however, increase the manufacturing time and cost of the media transport systems.
It would thus be, highly desirable to have a relatively simple and cost effective device for optimally guiding the sheet into the nip, thereby reducing the drive force required for driving the sheet along the media transport path while simultaneously allowing cost effective manufacturing methods and tolerances.